Apparatus for removing pollutants from stack effluents

ABSTRACT

A series of controlled gradient condensers for removing gaseous hydrocarbon pollutants from the stack effluent of an industrial treating plant, such as a veneer dryer. The gaseous effluent stream is conducted from the industrial treating plant to a precooler to bring the effluent temperature to the condensation point of the highest boiling pollutant. Thereafter the effluent stream is passed through a successive series of controlled gradient condenser, each operating in a temperature range lower than that of the immediately preceding condenser. The first several condensers are air cooled and designed to remove the higher boiling pollutants. Each air cooled condenser is wrapped with one or more heater coils, the turns of which are not uniformly wound about the condenser tubes but are more widely spaced toward the outlet or cold end of the condenser. Electric power to each heater coil is controlled by a respective power controller responsive to temperature sensors located inside the condenser for measuring a temperature gradient along the path of flow of the effluent. If any measured temperature gradient exceeds a predetermined maximum allowable limit, the power controller adjusts the electric power through the appropriate heater coil to restore the temperature gradient, and thus the cooling rate, to a value below the maximum limit. As long as the predetermined maximum temperature gradient or cooling rate for each gaseous pollutant is not exceeded the formation of aerosol is avoided and substantially all of the pollutant condenses in collectable liquid form on the walls of the condenser, thereby cleansing the effluent. Each condenser has a reservoir which collects the condensed pollutants by gravity feed, while the uncondensed remaining effluent passes to the next succeeding condenser. The last in the series of condensers is water cooled for condensing those pollutants having the lowest boiling points. The temperature gradient in the water cooled condenser is controlled by temperature sensors, similar to those in the air cooled condensers, which modulate the flow of coolant by controlling the power to the coolant pump. The different temperature ranges at which the respective condensers operate are preferably fixed so that the minimum temperature at the outlet of a respective condenser is greater than the highest melting point of any pollutant condensed within that condenser, so as to prevent solidification of the pollutants and fouling of the condensers. Immersion heaters in the condenser reservoirs further aid in preventing solidification. If solidification of one or more pollutants collected in a particular condenser cannot be avoided, scraper paddles are provided to scrape the solid material off the condenser walls for disposal through a solids removal port. The reservoir of the last in the series of condensers, from which the remaining effluent is vented to the atmosphere, includes a reservoir auxiliary cooling system for the purpose of further reducing effluent temperature if necessary to remove any remaining contaminants.

United States Patent n 1 Baum [ 1 Oct. 23, 1973 APPARATUS FOR REMOVINGPOLLUTANTS FROM STACK EFFLUENTS ['76] Inventor: Edward J. Baum, 1900S.W.

Pheasant Dr., Aloha, Oreg. 97005 [22] Filed: May 13, 1971 [21] Appl.No.: 143,125

[52] U.S. Cl. 165/1, 165/111, 55/82 3/1972 Dizio 55/82 PrimaryExaminer-Charles Sukalo Att0rney--Daniel P. Chernoff and Jacob E.Vilhauer [57] ABSTRACT A series of controlled gradient condensers forremoving gaseous hydrocarbon pollutants from the stack eflutants TEachair cooled condenser is wrapped with one or more heater coils, the turnsof which are not uniformly wound about the condenser tubes but are morewidely spaced toward the outlet or cold end of the condenser. Electricpower to each heater coil is controlled by a respective power controllerresponsive to temperature sensors located inside the condenser formeasuring a temperature gradient along the path of flow of the effluent.If any measured temperature gradient exceeds a predetermined maximumallowable limit, the power controller adjusts the electric power throughthe appropriate heater coil to restore the temperature gradient, andthus the cooling rate, to a value below the maximum limit. As long asthe predetermined maximum temperature gradient or cooling rate for eachgaseous pollutant is not exceeded the formation of aerosol is avoidedand substantially all of the pollutant condenses in collectable liquidform on the walls of the condenser, thereby cleansing the effluent. Eachcondenser has a reservoir which collects the V condensed pollutants bygravity feed, while the uncondensed remaining effluent passes to thenext succeeding condenser. The last in the series of condensers is watercooled for condensing those pollutants having the lowest boiling points.The temperature gradient in the water cooled condenser is controlled bytemperature sensors, similar to those in the air cooled condensers,which modulate the flow of coolant by controlling the power to thecoolant pump. The different temperature ranges at which the respectivecondensers operate are preferably fixed so that the minimum temperatureat the outlet of a respective condenser is greater than the highestmelting point of any pollutant condensed within that condenser, so as toprevent solidification of the pollutants and fouling of the condensers.Immersion heaters in the condenser reservoirs further aid in preventingsolidification. lf solidification of one or more pollutants collected ina particular condenser cannot be avoided, scraper paddles are providedto scrape the solid material off the condenser walls for disposalthrough a solids removal port. The reservoir of the last in'the seriesof condensers, from which the remaining effluent is vented to theatmosphere, includes a reservoir auxiliary cooling system for thepurpose of further reducing effluent temperature if necessary to removeany remaining contaminants.

17 Claims, 2 Drawing Flgures United States Patent [.1 1 [111 3,766,971Baum 0ct. 23,1973

APPARATUS FOR REMOVING POLLUTANTS FROM STACK EFFLUENTS BACKGROUND OF THElNVENTlON This invention relates to an improvement in apparatus forpurifying the stack effluent of an industrial treating plant before theeffluent is vented to the atmosphere. More specifically, the apparatusis of the type comprising a series of flow-through gradient condensersfor gradually cooling the effluent and condensing and removing thepollutants in liquid or semi-solid form. In addition to effluentpurification, the system may be useful for other commercial applicationsuch as gas liquefication.

in the past a number of methods for cleaning hydrocarbon emissions fromstackeffluents have been utilized. These include such methods asincineration, catalytic oxidation, scrubbing, activated carbonabsorption, and high energy filtration. Each of these systems hascertain inherent drawbacks, either with respect to economy oreffectiveness.

industrial condensers have long been utilized for condensing andcollecting various components of gaseous mixtures, but these systems arenot effective for accomplishing the complete cleansing of a gaseouseffluent. The reason for this is that conventional condensers do nothave temperature gradientor cooling rate control and tend to cool gasestoo rapidly as the gas flows through the condenser. When cooling is toorapid the gaseous components condense in the form of suspended aerosoldroplets, a large portion of which are carried along in the effluentstream and vented from the condenser without collecting on the condenserwalls. While such systems might be satisfactory for certain commercialuses, where the material being collected rather than the purity of thegas emitted from the condenser is of primary importance, such systemsare not suitable for effluent purification purposes. In fact it is oftennecessary that other purification devices be used in conjunction withsuch systems to control aerosol.

Some types of condensers, for example those utilizing liquid coolantcounterflow systems, are characterized by an impressed temperaturegradient between the inlet and outlet ends of the condenser. However,the temperature gradient is not controlled and is merely a result,rather than a cause, of the thermodynamic characteristics of thecondenser. No controlled temperature gradient or cooling rate isestablished along the path of flow of the gaseous effluent to preventthe undesirable formation of aerosol.

SUMMARY OF THE PRESENT INVENTION spective temperature range. The firstor highest tem-- perature condenser is preceded by a precooler, ifnecessary, to bring the effluent temperature down to the condensationpoint of the highest boiling pollutant. Each of the condensers isprovided with means for preventing the substantial formation of aerosolby controlling the maximum cooling rate of the effluent, particularly inthose temperature ranges corresponding to specific condensation pointsof pollutants known to be present in the effluent. The highertemperature air cooled condensers control the cooling rate by utilizingone or more heater coils wrapped about the condenser, the turns of whichare not uniformly wound but are more widely spaced toward the cold oroutlet end of the condenser. The electrical power to each heater coil iscontrolled by a power controller responsive to temperature sensorslocated inside the condenser wall for sensing the temperaturedifferential along the effluent stream. If the temperature differentialexceeds a predetermined maximum limit, the power controller adjusts thepower to the heater coils to restore the differential, and thus thecooling rate, to within the maximum limit. As an alternative to thetemperature sensors, or as an overriding control in addition thereto, anaerosol monitor in the condenser measures the formation of aerosol andadjusts the power supply to the heater coils to reduce the cooling ratewhen the aerosol count rate exceeds a predetermined limit. The lowertemperature condensers are preferably liquid cooled, with the coolingrate controlled by temperature sensors or aerosol monitors whichmodulate the flow of coolant by con trolling the power to the coolantpump.

The temperature ranges of the various condensers are preferably set sothat the minimum temperature of the effluent in each condenseris greaterthan that necessary to solidify the highest melting pollutant condensedwithin that particular condenser, so as to avoid fouling of thecondensers. In addition. the condenser reservoirs, where the pollutantsare collected in liquid form, preferably include immersion heaters tofurther prevent solidification. Where solidification of one or more ofthe pollutants collected in a particular condenser cannot be avoided,mechanically driven scraper paddles are provided to remove such solidsfrom the condenser walls. The last in the series of condensers, fromwhich the purified effluent is vented to the atmosphere, is providedwith a reservoir auxiliary cooling system for, the purpose of furtherreducing effluent temperatures if necessary to remove any remaininghydrocarbon contaminants. The degree of auxiliary cooling is controlledby a monitor which measures remaining hydrocarbon concentrations at thepoint where the effluent is vented to the atmosphere.

The novel features of the present invention provide it with a number ofimportant characteristics necessary to overcome the economic andoperational deficiencies of those purification and condenser devicespreviously described. Significant among these novel features is theprovision of gradient cooling control in the condensers, ensuring thateach pollutant is condensed at a cooling rate insufficient to'allow thesubstantial formation of aerosol droplets. As a result substantially allof the condensed pollutants are in fact collected by the condensers andremoved from the gaseous effluent rather than remaining suspended in theeffluent stream.

Moreover the provision of multiple flow-through condensers in series,each operating in a successively lower predetermined temperature range,facilitates the collection of at least most of the pollutants in liquidrather than solid form. This feature minimizes the fouling of thecondensers, reduces maintenance costs, and allows economic disposal ofthe waste products. The

provision of heated reservoirs and solids removal apparatus where neededfurther helps to achieve these objectives.

Furthermore the provision of an auxiliary cooling system in thereservoir of the final condenser, operating in response to a hydrocarbonconcentration monitor, provides a final safeguard by continually testingthe effectiveness of the system and improving the purity of theeffluent, if necessary, prior to its release into the atmosphere.

The foregoing and other objectives, features and advantages of thepresent invention will be more readily understood upon consideration ofthe following detailed description of the invention taken in conjunctionwith the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a schematic side elevationview of an illustrative embodiment of the condenser system including aprecooler.

FIG. 2 is a schematic view of a preheater which, in one embodiment ofthe invention, replaces the precooler of FIG. 1.

DESCRIPTION OF THE PREFERRED EMBODIMENT The effluent purifying system ofFIG. 1 comprises essentially two air cooled flow-through gradientcondensers l2 and and 14 connected in series by insulated effluentconduit 10, followed by a water cooled gradient condenser 16. Aprecooler l8 precedes the series of condensers.

The purpose of the condensers is to remove the hydrocarbon pollutantsfrom the stack effluent of an industrial treating plant such as a veneerdryer (not shown) before the effluent is vented to the atmosphere. Thegases enter the system at port and pass consecutively through thecondensers, which gradually cool the effluent and thereby liquify andremove the various pollutants. The remaining purified effluent is ventedto the atmosphere through outlet port 22 of the final condenser 16.

The number and type of consecutive condensers utilized, the temperaturerange through which each condenser cools'the effluent, and the necessityfor precooler 18 are all determined by the initial composition andtemperature of the effluent emitted from the industrial treating plant.By way of illustration, assume that a treating plant emits effluent at500F containing the following hypothetical hydrocarbon pollutants Athrough E, with boiling and melting points adjusted to allow foroperating pressures in the condensers:

Pollutant Boiling Point Melting Point A 400F 275 Since the effluent isemitted from the treating plant at a temperature considerably higherthan the boiling point of the highest boiling pollutant A, it isdesirable that a precooler 18 bring the effluent temperature down to400F before the effluent enters the first condenser 12. This avoids theexpense of providing condenser 12 with extra cooling capacity. If thetemperature at which the effluent is emitted were lower than the boilingpoint of pollutant A it would be desirable to incorporate a preheater,rather than a precooler, in advance of condenser 12 to maintain theeffluent at least at the temperature at which it is emitted from thetreating plant before it enters condenser 12. In any case thetemperature at which the effluent enters the first condenser 12 shouldpreferably be at or below the boiling point of the highest boilingcontaminant to be removed from the effluent.

The lowest temperature to which condenser 12 cools the effluent shouldbe greater than the highest melting point of any pollutant condensedtherein, so as to avoid solidification of the pollutant and fouling ofthe condenser. Therefore the temperature at which the effluent leavescondenser 12 should be higher than the melting point of pollutant A, say300F. Since pollutant A" is an exceptionally high melting compound,forming tars at a temperature higher than the boiling points of theother pollutants, only A is collected in condenser 12 and furthercondensers must be provided to remove the other pollutants.

The second air cooled condenser 14 cools the effluent from thetemperature at which it was exhausted from condenser 12 to an exittemperature which, again, is preferably higher than the highest meltingpoint of any pollutant condensed in condenser 14. Since, for reasons ofcompactness, it is less desirable to condense by air cooling below 212,condenser 14 operates between 300Fand 212F, condensing and removingpollutants B and C with no problem of solidification. Thereafter a watercooled condenser 16 condenses lower boiling pollutants D and E in thetemperature range from 212F to 60F.

It may be that the gaseous effluent of the treating plant containsadditional pollutants having respective boiling and melting points suchthat it is economically impractical to avoid the solidification problem.In such case a solids removal device, tobe described hereafter indetail, is included in any condenser where one or more pollutants iscollected and cooled below its melting point.

Having described the general operation of the effluent purifyingapparatus, the features of the individual components of the system willnow be described in detail. By way of general definition it should bepointed out that the various power controllers described in thefollowing text may comprise any of a number of commercially availableelectrical control devicessuch as silicon controlled rectifiers operatedalone or in parallel responsive to control signals generated in anamplified measuring circuit. The measuring circuit itself mightincorporate a differential voltage comparator comprising operationalamplifier circuits. Furthermore the temperature sensors describedhereafter may comprise any suitable electrical sensor such as athermocouple or thermistor. All inlet and outlet ports as well as allconduits joining the various components of the system are preferablyinsulated to minimize heat transfer and uncontrolled cooling.

Precooler 18 has an electrically powered fan 26 which forces ambienttemperature air into chamber 24, where the air mixes with and cools theraw gaseous effluent entering the chamber through port 20. The rate ofair coolant feed is controlled by a power controller 28 which modulatesthe electric power supplied to fan 26 in response to signals receivedfrom an effluent temperature sensor 30. If the effluent temperature atthe outlet of precooler l8 exceeds the desired inlet temperature of thefirst condenser 12, sensor 30 causes controller 28 to increase the powerto fan 26, thereby increasing the rate of coolant feed. Conversely ifthe precooler outlet temperature is too low, controller 28 reduces thepower to fan 26.

If temperature maintanance rather than precooling of the effluent isnecessary, as explained above, a preheater 32 as shown in FIG. 2 mightreplace precooler 18 if desired. Preheater 32 has an inlet port athrough which the effluent from the treating plant enters. At outlet 34,which connects to the inlet end of the first condenser 12, a temperaturesensor 36 monitors the temperature of the effluent and controls thepower supplied to electric heater coil 41 through power controller 38.If the temperature measured by sensor 36 falls below the desired value,power control 38 increases the power to heater coil 41, and converselyif the temperature rises above the desired value, the power is reduced.

Condensers 12 and 14 are both preferably of the air cooled cross-flowtype since they are designed to operate in relatively high temperatureranges. Each con-. denser may comprise either one or a bundle ofcondenser tubes 40, 40a respectively, and each may or may not be cooledby a forced air system, depending upon the desired cooling range of eachcondenser and the practical length and cross section of the condensertubes.

A significant feature of both air cooled condensers is that they includemeans for controlling the maximum rate at which the effluent streampassing through them is cooled. This control is established by heatercoils 42, 42a wrapped about the respective condenser tubes, the turns ofwhich are preferably not uniformly wound but are more widely spacedtoward the cold or outlet end of the respective condensers. When poweris applied to the coils they emit heat which, because of the unevenwinding, tends to raise the temperature of the condenser walls unevenly,more toward the upstream end of the condenser than the downstream end.This causes a temperature gradient to be imposed along the condenserwalls and results in an overall reduction in the cooling rate, i.e., therate at which heat is extracted from the effluent. An increase in powerapplied to the is passed through a condenser tube at a high flow rate,and if heat is removed too quickly by impressing an excessively coldtemperature on the gas, the gas will condense in the form of suspendedaerosol droplets throughout the cross section of the stream rather thancondensing merely in those regions close to the condenser walls. If thishappens a large portion of the aerosol will be swept through thecondenser tube too quickly to migrate toward the walls and collectthereon, and will be vented from the condenser without It is arecognized phenomenon that if a stream of gas being collected andremoved. However for any specific gaseous compound flowing through aparticular condenser at a particular flow rate, a maximum allowablecooling rate can be experimentally established, above whichuncollectable amounts of aerosol are observed to form in the condenser,and below which substantially no aerosol is formed and the compoundcondenses on the condenser walls. Such experimentation can be performedby gradually increasing the power to a heater coil such as 42 whileobserving visually or by means of an aerosol monitor that point wherethe cooling rate is sufficiently reduced that aerosol formation in thecondenser is minimized and condensate collection is maximized. Thatpoint establishes the maximum allowable cooling rate, which canthereafter be controlled by controlling the impressed temperaturegradient along the path of flow of the effluent by modulating the powerto heater coils 42 and 42a so as to stay within the maximum coolingrate.

Electrical power to heater coils 42, 42a can be controlled by any ofseveral methods. For example heater coil 42 is controlled by a powercontroller 44 in re sponse to an aerosol monitor 46, such as apiezoelectric oscillator, which samples the effluent stream andgenerates an emf proportional to an aerosol count rate. Upon sensing acount rate above a desirable level, aerosol monitor 46 causes powercontroller 44 to increase the electrical power to heater coil 42,thereby decreasing the cooling rate along the path of flow of theeffluent. As long as the count rate is within desirable limits powercontroller 44 supplies as little power as possible to heater 42 tomaximize the cooling rate without thereby increasing the formation ofaerosol to beyond desired limits.

An alternative method of controlling the maximum cooling rate is shownwith respect to condenser 14 where the power to heater coil 42a ismodulated by power controller 44a in response to a temperaturedifferential in the effluent stream measured by temperature sensors 48and 50. If the measured temperature differential, which is proportionalto the cooling rate of the effluent, exceeds a predetermined limit,power controller 44a increases the electrical power to heater coil 42ato restore the temperature differential to within the maximum limit. Aslong as the maximum temperature differential is not exceeded, powercontroller 44a delivers as little power as possible to heater 42a tomaintain the maximum allowable cooling rate.

It is also conceivable that primary control could be effected bytemperature sensors such as 48 and 50 with an aerosol monitor such as 46acting as an overriding control in addition to the temperature sensors.

One or more independent heater coils may be used along the length ofeach condenser tube 40, 40a, depending on the precision of controlrequired. Since the effluent temperature drops steadily from the inletto the outlet end of each condenser, condensation of some of thepollutants may take place in different regions along the length of eachcondenser depending upon where the effluent temperature corresponds tothe boiling point of the particular pollutant. Since some of thepollutants may have different optimum cooling rates than others, it maybe desirable to install multiple heater coil and power controllersystems on a particular condenser to achieve controlled effluent coolingseparately with respect to the different condensation regions.

The water cooled gradient condenser 16 controls the maximum effluentcooling rate by a method which differs somewhat from air cooledcondensers 12 and 14. The gaseous effluent flowing through the tubes 52of condenser 16 is cooled by a counterflow of water, pumped through thejacket 53 of the condenser by electrically powered pump 54 and emptiedthrough port 56. The rate of cooling depends on the flow rate at whichthe coolant is pumped through the condenser by pump 54. A group oftemperature sensors 58 and a corresponding group of sensors 60continually monitor the effluent temperature gradient, and if thegradient 1 exceeds a predetermined level, indicating an excessivecooling rate, the sensors cause power controller 62 to reduce theelectrical power supplied to pump 54, thereby slowing the flow ofcoolant and reducing the cooling rate. Power controller 62 normallysupplies as much power as possible to pump 54 without thereby exceedingthe predetermined maximum temperature gradient. Alternatively totemperature sensors 58 and 60, it is conceivable that an aerosol monitorsuch as 46 could sample the effluent stream to control the power supplyto pump 54. Obviously the method of cooling control utilized withrespect to condenser 16 could be applied to any condenser using forcedfluid cooling, such as a forced air condenser.

Each of the condensers has its own separate reservoir which collects thecondensed pollutants by gravity feed. If high effluent speeds areattained in the condenser pipes each reservoir is preferably constructedof 30 sufficient diameter, and the amount of condensate in the reservoiris kept sufficiently low, by continuous removal thereof, that the lineareffluent velocity through the reservoirs is reduced below that at whichdust, solids or liquid may be swept out. Reservoir 64 of condenser 12 isdesigned to collect high boiling pollutants in liquid form only. Thereservoir is equipped with a condensate removal valve 66 and animmersion heater 68 which ensures that the liquid condensate does notcool below the melting point of any of the contaminants.

Condenser 14 on the other hand is equipped to collect contaminants bothin liquid and solid form. Such provision must be made whensolidification of some contaminants within a particular condenser cannotbe economically avoided. Condenser 14 is equipped with scraper paddles70 rotatably driven by a motor 72 at moderate speed. The paddles arespring biased against the inner walls of the condenser, and theirrotation tends to scrape any solidified pollutants off the walls anddrop them into reservoir 76. The reservoir has a discharge valve 78comprising a series of driven rotating paddles 74 through which both thesolids and liquids collecting in the reservoir are removed. Reservoir 76isfurther equipped with an immersion heater 82 similar to 68, forpreventing solidification of the liquid in the reservoir.

Reservoir 86 of water cooled condenser 16 is the place from which thepurified effluent, having passed through all condensation steps, isvented to the atmosphere. Because of this fact, and because the lowerboiling pollutants in reservoir 86 generally have very low meltingpoints with no danger of solidification, reservoir 86 is equipped withan auxiliary cooling or refrigeration system rather than a heater. Inits simplest form the cooling system comprises immersed coil 88 throughwhich electric pump 90 forces a stream of cooling water. The degree ofcooling is determined by the flow rate of coolant through coil 88 Apower controller 92 modulates the coolant flow rate in response to ahydrocarbon concentration monitor 94, such as a total hydrocarbonanalyzer or flame ionization detector, which tests the purity of theeffluent stream just before it is vented to the atmosphere. If themonitor 94 detects hydrocarbon concentrations in excess of apredetermined maximum limit, possibly determined by governmentregulation, the power controller 92 increases the rate of coolant flowthrough coil 88 thereby lowering the temperature of the liquid in thereservoir. This further reduces the effluenttemperature and reduces thevapor pressures of the remaining contaminants to the point where theywill condense and be collected in reservoir 86 prior to the emission ofthe effluent into the atmosphere. If a more elaborate refrigerationsystem were used instead of the water cooled system shown in FIG. 1,power controller 92 could modulate cooling either through compressorpower control or refrigerant flow control.

The terms and expressions which have been employed in the foregoingabstract and specification are used therein as terms of description andnot of limitation, and there is no intention, in the use of such termsand expressions, of excluding equivalents of the features shown anddescribed or portions thereof, it being recognized that the scope of theinvention is defined and limited only by the claims which follow.

What is claimed is:

1. A method of removing components from a stream of gaseous effluentwhich comprises:

a. gradually extracting heat from the effluent by cooling the effluentthrough the boiling points of the various components to be removed,thereby condensing the components;

b. monitoring the amount of said components condensed in the form ofaerosol; and

c. reducing the rate at which heat is extracted from the effluentwhenever the amount of said components condensed in the form of aerosolexceeds a predetermined limit.

2. A method of removing a component from a stream of gaseous effluent bygradually cooling the stream and liquefying the component whichcomprises:

a. determining a maximum rate of cooling for the stream above which theamount of aerosol formed in said stream by said cooling exceeds apredetermined limit; and

b. gradually cooling said stream through the boiling point of saidcomponent at a controlled rate of cooling within said maximum rate ofcooling.

3. The method of claim 2, wherein the cooling step (b) comprises:

measuring the rate at which said effluent stream is being cooled; and

reducing the rate at which said effluent stream is cooled when themeasured cooling rate exceeds said predetermined maximum cooling rate.

4. The method of claim 2, further comprising:

precooling the stream of effluent in advance of cooling step (b) down tothe boiling point of the highest boiling component therein.

5. The method of claim 2, further comprising:

measuring the concentration of said component in the effluent after thecooling step (b); and

further cooling said effluent stream if such component concentration isin excess of a predetermined limit.

6. A method of removing pollutants from a stream of gaseous stackeffluent before such effluent is vented to the atmosphere whichcomprises:

a. gradually cooling the effluent stream through the boiling points ofthe various pollutants to be removed, thereby condensing and separatingsuch pollutants from said effluent;

b. measuring the pollutant concentration in the effluent after suchcooling step;

c. further cooling said effluent stream prior to venting it to theatmosphere if such pollutant concentration is in excess of apredetermined limit.

7. A method of removing pollutants from the gaseous stack effluent of anindustrial treating plant, said pollutants having different boiling andmelting points and a first one of said pollutants having a boiling pointand a melting point higher than the boiling point of a second one ofsaid pollutants, which method comprises:

a. cooling said effluent to the boiling point of said first pollutant toliquefy said first pollutant;

b. further cooling said effluent toward the boiling point of said secondpollutant;

c. removing said first pollutant from said effluent in liquid formbefore said effluent is cooled to the boiling point of said secondpollutant.

8. The method of claim 1 wherein said first pollutant is removed fromsaid effluent before said effluent is cooled to the melting point ofsaid first pollutant.

9. The method of claim 1 wherein said cooling step (a) is accomplishedby passing said effluent stream through a condenser, and wherein saidcooling rate reduction step (c) is accomplished by emitting heatadjacent said gaseous effluent stream to counteract the cooling of saidstream by said condenser.

10. The method of claim 9, further comprising exposing a piezoelectricoscillator to said effluent stream for measuring an aerosol count ratein said stream and uti-- lizing said piezoelectric oscillator togenerate an emf in proportion to said count rate for controlling theemission of said heat.

ll. The method of claim 2 wherein said cooling step (b) is accomplishedby passing said stream through a condenser and wherein said rate ofcooling is controlled by emitting heat adjacent to said stream tocounteract the cooling of said stream by said condenser.

12. The method of claim 11 wherein a greater concentration of heat isemitted toward the upstream end of said condenser where said effluentstream enters than toward the downstream end, so as to cause a reductionin cooling rate which is greater toward the upstream end than toward thedownstream end of said condenser.

13. The method of claim 2 wherein said cooling step (b) is accomplishedby passing said stream through a condenser of the type which cools saideffluent stream by means of a flow of coolant, and wherein said coolingrate is controlled by controlling the rate of flow of said coolant.

14. The method of claim 2, further comprising preheating the stream ofeffluent in advance of cooling step (b) to maintain the temperature ofsaid stream at substantially the boiling point of the highest boilingcomponent therein.

15. The method of claim 3 wherein the rate at which said effluent streamis cooled is measured by means of a pair of temperature sensors locateda spaced distance apart along the path of flow of said stream to measurethe temperature differential of said stream between said temperaturesensors.

16. The method of claim 7 including the step of supplying heat to saidfirst pollutant after it has been removed from said effluent so as toprevent solidification of said first pollutant.

17. The method of claim 7 wherein said effluent is cooled by passing itthrough a condenser and wherein said first pollutant is removed fromsaid effluent by collecting it in a reservoir located at a point alongthe path of travel of said effluent through said condenser in advance ofthe point where said condenser cools said effluent to the melting pointof said first pollutant.

1. A method of removing components from a stream of gaseous effluentwhich comprises: a. gradually extracting heat from the effluent bycooling the effluent through the boiling points of the variouscomponents to be removed, thereby condensing the components; b.monitoring the amount of said components condensed in the form ofaerosol; and c. reducing the rate at which heat is extracted from theeffluent whenever the amount of said components condensed in the form ofaerosol exceeds a predetermined limit.
 2. A method of removing acomponent from a stream of gaseous effluent by gradually cooling thestream and liquefying the component which comprises: a. determining amaximum rate of cooling for the stream above which the amount of aerosolformed in said stream by said cooling exceeds a predetermined limit; andb. gradually cooling said stream through the boiling point of saidcomponent at a controlled rate of cooling within said maximum rate ofcooling.
 3. The method of claim 2, wherein the cooling step (b)comprises: measuring the rate at which said effluent stream is beingcooled; and reducing the rate at which said effluent stream is cooledwhen the measured cooling rate exceeds said predetermined maximumcooling rate.
 4. The method of claim 2, further comprising: precoolingthe stream of effluent in advance of cooling step (b) down to theboiling point of the highest boiling component therein.
 5. The method ofclaim 2, further comprising: measuring the concentration of saidcomponent in the effluent after the cooling step (b); and furthercooling said effluent stream if such component concentration is inexcess of a predetermined limit.
 6. A method of removing pollutants froma stream of gaseous stack effluent before such effluent is vented to theatmosphere which comprises: a. gradually cooling the effluent streamthrough the boiling points of the various pollutants to be removed,thereby condensing and separating such pollutants from said effluent; b.measuring the pollutant concentration in the effluent after such coolingstep; c. further cooling said effluent stream prior to venting it to theatmosphere if such pollutant concentration is in excess of apredetermined limit.
 7. A method of removing pollutants from the gaseousstack effluent of an industrial treating plant, said pollutants havingdifferent boiling and melting points and a first one of said pollutantshaving a boiling point and a melting point higher than the boiling pointof a second one of said pollutants, which method comprises: a. coolingsaid effluent to the boiling point of said first pollutant to liquefysaid first pollutant; b. further cooling said effluent toward theboiling point of said second pollutant; c. removing said first pollutantfrom said effluent in liquid form before said effluent is cooled to theboiling point of said second pollutant.
 8. The method of claim 7 whereinsaid first pollutant is reMoved from said effluent before said effluentis cooled to the melting point of said first pollutant.
 9. The method ofclaim 1 wherein said cooling step (a) is accomplished by passing saideffluent stream through a condenser, and wherein said cooling ratereduction step (c) is accomplished by emitting heat adjacent saidgaseous effluent stream to counteract the cooling of said stream by saidcondenser.
 10. The method of claim 9, further comprising exposing apiezoelectric oscillator to said effluent stream for measuring anaerosol count rate in said stream and utilizing said piezoelectricoscillator to generate an emf in proportion to said count rate forcontrolling the emission of said heat.
 11. The method of claim 2 whereinsaid cooling step (b) is accomplished by passing said stream through acondenser and wherein said rate of cooling is controlled by emittingheat adjacent to said stream to counteract the cooling of said stream bysaid condenser.
 12. The method of claim 11 wherein a greaterconcentration of heat is emitted toward the upstream end of saidcondenser where said effluent stream enters than toward the downstreamend, so as to cause a reduction in cooling rate which is greater towardthe upstream end than toward the downstream end of said condenser. 13.The method of claim 2 wherein said cooling step (b) is accomplished bypassing said stream through a condenser of the type which cools saideffluent stream by means of a flow of coolant, and wherein said coolingrate is controlled by controlling the rate of flow of said coolant. 14.The method of claim 2, further comprising preheating the stream ofeffluent in advance of cooling step (b) to maintain the temperature ofsaid stream at substantially the boiling point of the highest boilingcomponent therein.
 15. The method of claim 3 wherein the rate at whichsaid effluent stream is cooled is measured by means of a pair oftemperature sensors located a spaced distance apart along the path offlow of said stream to measure the temperature differential of saidstream between said temperature sensors.
 16. The method of claim 7including the step of supplying heat to said first pollutant after ithas been removed from said effluent so as to prevent solidification ofsaid first pollutant.
 17. The method of claim 7 wherein said effluent iscooled by passing it through a condenser and wherein said firstpollutant is removed from said effluent by collecting it in a reservoirlocated at a point along the path of travel of said effluent throughsaid condenser in advance of the point where said condenser cools saideffluent to the melting point of said first pollutant.